1. Field of the Invention
The present invention relates to a method of manufacturing a liquid crystal display device, and particularly relates to a method of manufacturing a liquid crystal display device solving a pattern defect caused by a foreign substance which attaches in the process of manufacturing.
2. Description of the Related Art
Cases where a liquid crystal display device is used as a flat panel display having advantages of its lightweight and slimness are increasingly expanding. As the cases expand, the liquid crystal display device is desired to further improve its display performance. Improvements of the display performance indicate higher brightness, definition, response speed and the like. In addition, as improvements of the display quality, display defects such as defects by bright and dark dots are strongly desired to be solved. The bright dot is a phenomenon in which a gray scale display in response to an applied voltage cannot be shown even if the applied voltage is changed, and a pixel looks white since the pixel is always on. The defect by a dark dot is a phenomenon in which a gray scale display in response to the applied voltage cannot be shown even if the applied voltage is changed, and a pixel looks black since the pixel is always off. One of causes triggering such display defects is an admixture of foreign substances in the manufacturing process.
When patterning by using a photolithography technique, coating of photoresist material, exposure and development are performed. If a foreign substance is attached before this coating or exposure, unevenness of coating, uneven amount of exposure, or the like is caused on a spot where the foreign substance has attached. Thus, a photoresist remains in an area where the photoresist should not remain on a design basis. Furthermore, a spot upon development is also considered. When such a remaining photoresist and a spot upon development occur, a pattern defect is caused if etching is performed by using such a photoresist pattern as a mask and the photoresist pattern is thereafter removed. Due to this pattern defect, conductive patterns, which should be separated, are connected, thus causing a short circuit. Moreover, if a residual pattern appears in an area where it should not exist on a design basis, the pattern comes into contact with electrodes or lines in its vicinity, which may trigger a short between electrodes or between lines.
As a method of repairing a liquid crystal display device in which such a display defect occurs, a laser irradiation method has been proposed. For example, a laser is irradiated to the electrode line of a pixel having a bright dot so that the pixel is repaired to always display in black. Please refer to Japanese Laid-open Patent No. 2002-318393 and Japanese Laid-open Patent No. 2004-070182. As a display defect, a pixel of a black display, which is always off, is less noticeable compared with a pixel which is always on. Therefore, a display defect can be eased by being repaired in a manner of making it a black display.
However, in the repairing method of a laser irradiation for a display defect, it is required to repair bright and dark dots by performing an inspection which a drive voltage is supplied to a liquid crystal display device in order to cause the device to perform a display operation, and by identifying a pixel having a display defect. In this case, when there is a short circuit or capacitance coupling in a semiconductor film with a low resistance even when measured by electric characteristics, it may not be possible to detect a defect since inspection capacity is low. In addition, if only the repairing method of a laser irradiation for a display defect is dependable, an active matrix substrate containing a pattern defect, which is a display defect, is considered to be a conforming item. Thus, the manufacturing is progressed to a step of bonding the substrate and a counter substrate together to form a liquid crystal display panel. Accordingly, a defective component is flowed out to downstream processes, thus causing an increase in fraction defective.
It is desired to solve a pattern defect area in a step where the pattern defect occurs. As a method of solving the pattern defect in the step where the pattern defect occurs, it is considered to firstly etch and then remove a conductive pattern formed by patterning a conductive film, when the pattern defect is found. After removing the conductive pattern once, a conductive film is formed anew, and a plurality of conductive patterns are then formed by patterning. However, the number of manufacturing steps increases dramatically in such a repairing method.